This invention relates to the formulation of color photographic papers. It particularly relates to the formulation of photographic papers having less upper scale haze, improved resistance to dry scratching, and excellent slip characteristics before and after photographic processing.
A property of photographic papers that is of interest is to have a slip agent in the layer furthest from the support to improve the papers resistance to scratching and emulsion pressure sensitivity. Furthermore it is desirable to have overcoat lubricants that provide good slip properties and resistance to dry scratching in the processed photograph. Papers without adequate lubricity can cause sticking problems during conveyance through photoprocessing equipment, especially in minilabs where smooth metallic and glass surfaces contact the emulsion surface. Emulsion to backside lubricity is desired for post processing print stacking operations that occur on many minilabs. The overcoat lubricant is most effective when it is present in the top layer on the emulsion side.
These lubricants typically are agents that are insoluble in aqueous media. They may be dissolved in high boiling organic solvents, and this mixture is mixed under high shear or turbulence together with an aqueous medium to form a dispersion. The overcoat lubricant dispersions can cause a light scatter problem when they are present at the surface of the coating. The amount of light scatter is dependent on the match of the complex refractive indexes between the overcoat lubricant dispersion and the surrounding hydrophilic colloid media, as well as the particle size of the dispersion. Typically this light scatter problem is most prevalent at very high print densities, where very little light is reflected back to the viewer. Any diffuse angle first surface reflection present in the coating limits the density that can be measured, or seen by the eye at a diffuse angle relative to the angle of illumination. This first surface reflection phenomenon is typically referred to as xe2x80x9chazexe2x80x9d. Reducing the particle size of the overcoat lubricant dispersion on the surface of the coating can result in a haze improvement and it effectively increases the reflection limit of the print, but it also causes a loss in lubricity, requiring more lubricant to achieve the desired slip characteristics. The maximum print densities decrease as the lubricant levels are increased.
U.S. Pat. No. 5,208,139 describes a multilayer structure that contains colloidal silica with at least non-silver bearing layer and a non-silver bearing overcoat with lubricant. U.S. Pat. No. 5,019,491 describes a photo material with at least 1 light sensitive layer and at least 1 layer containing lubricant. U.S. Pat. No. 4,004,927 describes a photographic material containing a liquid organopolysiloxane. U.S. Pat. No. 4,499,179 describes oil particles in the top layer of a photographic element.
There is a continuing need for improved overcoat lubrication to provide resistance to scratching and improved slip properties in processed photographic paper. There is particularly a need for lubricants that will provide lubricity to photographic elements without causing an increase in light scatter that results in a hazy appearance, especially in dark areas of a photographic print.
An object of the invention is to overcome disadvantages of prior photographic papers.
It is another object of the invention to provide photographic papers having improved resistance to scratching and good slip properties.
A further object is to provide photographic papers with good lubricity and low haze in dark areas of the print.
These and other objects of the invention are generally accomplished by a photographic element comprising a reflection support and an overcoat layer wherein said overcoat layer comprises hydrophilic binder and lubricant, said lubricant has a particle mean volume diameter of greater than 1 xcexcm and the total volume of particles of lubricant below 1 xcexcm is less than 5% of said total volume of lubricant.
The invention has numerous advantages over prior techniques for providing lubricity to photographic elements. The photographic elements of the invention have low haze. Further the elements have good slip properties and resistance to dry scratching of the processed photograph. The invention also allows the use of less lubricant to achieve a given lubricity, thereby lowering cost and improving photographic properties.
With our invention we can achieve good slip properties at low lubricant coverages with very high maximum print densities (low haze) by using large particle sized dispersions of common overcoat lubricants. The examples that we have produced have very low friction coefficients with haze levels that matched model format coatings with no overcoat lubricant. We found that the advantages of large particle sized dispersions can be obtained by using a pre-mix of dispersion, where the particle size distribution is very broad, but the vast majority of the volume percent of the lubricant is present as droplets that are greater than 1 micron in diameter. A preferred embodiment of this invention is the use of emulsifying techniques that produce uniformly large droplets that are 1 to 12 xcexcm in average particle diameter. Limited coalescence is one emulsifying technique that can be employed to make narrow particle size distribution within this 1-12 micron size range.
In performing the invention, any suitable lubricant may be utilized. There is no limitation on the types of lubricants for the practice of the present invention. Typical lubricants include (1) silicone based materials disclosed, for example, in U.S. Pat. Nos. 3,489,567; 3,080,317; 3,042,522; 4,004,927; 4,047,958; and in British Patent Nos. 955,061 and 1,143,118; (2) higher fatty acids and derivatives, higher alcohols and derivatives, metal salts of higher fatty acids, higher fatty acid esters, higher fatty acid amides, polyhydric alcohol esters of higher fatty acids, etc., disclosed in U.S. Pat. Nos. 2,454,043; 2,732,305; 2,976,148; 3,206,311; 3,933,516; 2,588,765; 3,121,060; 3,502,473; 3,042,522; and 4,427,764, in British Patent Nos. 1,263,722; 1,198,387; 1,430,997; 1,466,304; 1,320,757; 1,320,565; and 1,320,756; and in German Patent Nos. 1,284,295; and 1,284,294; (3) liquid paraffin and paraffin or wax like materials such as carnauba wax, natural and synthetic waxes, petroleum waxes, mineral waxes and the like; (4) perfluoro- or fluoro- or fluorochloro-containing materials, which include poly(tetrafluoroethylene), poly(trifluorochloroethylene), poly(vinylidene fluoride, poly(trifluorochloroethylene-co-vinyl chloride), poly(meth)acrylates or poly(meth)acrylamides containing perfluoroalkyl side groups, and the like. Lubricants useful in the present invention are also described in further detail in Research Disclosure, No. 308, December 1989, page 1006, all of the above incorporated herein by reference.
The above lubricants also may contain reactive functional groups such as hydroxyl, thiol, carboxyl, carbodiimide, epoxy, aziridine, vinyl sulfone, sulfinic acid, active methylene, amino, and amide. Typical examples of compounds useful for the present invention are shown below, but the present invention is not limited by these compounds:
L-1. Carnauba Wax, Michelube 160 [Michelman Inc.]
L-2. Paraffin Wax 112/118 AMP, m.p.=46.1xc2x0 C. [Frank B. Ross Inc.]
L-3. Paraffin Wax 125/130 AMP, m.p.=53.3xc2x0 C. [Frank B. Ross Inc.]
L-4. Paraffin Wax 140/145 AMP, m.p.=61.1xc2x0 C. [Frank B. Ross Inc.]
L-5. Ross Wax 140, m.p.=137.8xc2x0 C. [Frank B. Ross Inc.]
L-6. Teflon 120, fluorinated ethylene propylene particles [E. I. du Pont de Nemours and Co.]
L-7. Teflon 30, poly(tetrafluoroethylene) particles [E. I. du Pont de Nemours and Co.]
L-8. Teflon 335, poly(tetrafluoroethylene-perfluoro(propyl vinyl ether)) particles [E. I. du Pont de Nemours and Co.]
L-9. GP-218 silicone polyol copolymer [Genesee Polymers Co.]
L-10. GP-4 silicone fluid, amine functionalized [Genesee Polymers Co.]
L-11. GP-7100 amine functional paintable silicone fluid [Genesee Polymers Co.]
L-12. GP-7200 silicone fluid, mercapto functionalized [Genesee Polymers Co.]
L-13. EXP-58 silicone wax [Genesee Polymers Co.]
L-14. EXP-61 silicone wax, amine functionalized [Genesee Polymers Co.]
L-15. EXP-77 silicone wax, mercapto functionalized [Genesee Polymers Co.]
L-16. GP-7101 silicone copolymer [Genesee Polymers Co.]
L-17. BYK-331, polyether modified di-methylpolysiloxane copolymer [BYK Chemie]
L-18. BYK-371, reactive silicone additive, an acrylic functional, polyester-modified dimethylpolysiloxane [BYK Chemie]
L-19. DC-200 silicone fluid [Dow Corning Inc.]
L-20. PS099 dimethylsiloxane-bisphenol A carbonate block copolymer [Petrarch Inc.]
L-21. PS130 polymethyloctadecylsiloxane [Petrarch Inc.]
L-22. PS135 poly(methylhexadecyl siloxane) [Petrarch Inc.]
L-23. PS-464 polydimethylsiloxane, vinylphenylmethyl terminated [Petrarch Inc.]
L-24. Sorbitan monostearate
L-25. Ethylene glycol distearate
L-26. Ethylene glycol monostearate
L-27. Potassium hexadecyl phosphate
L-28. Sodium hexdecanesulfonate
L-29. Lubracal 60, Calcium stearate
L-30. Sodium stearate
L-31. Lithium stearate
L-32. Glyceryl monostearate
A preferred lubricant has been found to be polydimethylsiloxane, as it is low in cost and effective.
The overcoat layer containing the lubricant of the invention also may contain other materials. Such other materials include polymeric gelatin extenders, fillers such as latexes and colloidal silica. The overcoat layer may also contain matte beads that provide ferrotyping and blocking protection. The overcoat layer may also contain UV light absorbing materials as described in U.S. Pat. Nos. 4,528,311; 4,611,061; 4,785,063; and 4,892,915.
The gelatin utilized in the overcoat layers of the invention may be any suitable gelatin. Typical of such gelatins are alkaline processed bone gelatin, acid processed pigskin gelatin, derivatized gelatin as outlined in U.S. Pat. Nos. 5,219,992 and 5,316,902. Preferred gelatins are acid processed ossein gelatins.
The lubricant particles may be any suitable size of greater than 1 xcexcm. Preferred are particles between about greater than 1 and 12 xcexcm as they provide good lubricity with minimal light scatter. A more preferred particle size is between about 1.5 and 7.5 xcexcm for good lubricity and the minimum light scatter. While the particle sizes referred to above are the mean diameter of the particles, it is also a feature of the invention that the lubricant particles of less than 1 xcexcm in diameter comprise less than 5% of the total volume of lubricant in the overcoat layers.
The lubricants of the invention are generally formed by any means that result in particles of the desired size distribution. A suitable method of formation is a limited coalescence technique as shown in U.S. Ser. No. 08/440,265 filed May 5, 1995. Other techniques of forming particles are described in Research Disclosure No. 37038, February 1995. Other effective techniques for making particles are described in P. Walstra xe2x80x9cThe Encyclopedia of Emulsion Technologyxe2x80x9d, Vol. 1, Chapter 2, pages 60-67 (1983).
The invention overcoat layer may be utilized in any photographic element. Typical of such elements are motion picture film, x-ray film, and color negative film. Preferred use of the invention is in color photographic paper as there is a particular need for improvement in lubricity without causing haze in the dark areas of a photographic print. The photographic paper materials may be formed by any of the conventional techniques available for forming such materials and may use any of the known materials for formation of color photographic papers. Typical of such materials are those disclosed in Research Disclosure No. 37038, February 1995.